1. Field of the Invention
The present invention relates to an organic EL display apparatus in which a self-emission organic EL (electroluminescence) element is used for each pixel and disposed in a matrix form, and more particularly to an organic EL display apparatus which is suitable for reduction of luminance variation of the individual pixels.
2. Description of the Related Art
The display apparatus using the organic EL elements has features not possessed by an LCD (liquid crystal display apparatus) because the organic EL elements are self-emission elements not requiring a backlight and appropriate for reduction of power consumption. It also has characteristics including a quick response and a wide viewing angle, and the element itself is solid, so that it has an advantage that it can be applied to flexible usage.
To drive the organic EL display apparatus, PM (passive matrix) drive and AM (active matrix) drive can be employed in the same manner as the LCD, but the AM drive method, which provides the individual pixels with a thin-film transistor (TFT) to separately control them, is the mainstream. Thus, the provision of high definition, long life and lower power consumption is also taken into consideration.
To control the emission of light by each pixel of the organic EL display apparatus without involving variation, it is necessary to provide the same current value to the individual pixels for a prescribed image signal. Especially, such control is important for a method that the image signal is given as an analog signal and the pixels are caused to emit an intermediate light according to its analog value. Examples of a display apparatus, which is intended to reduce luminance variation, include the following patent literatures 1 and 2.
The organic EL display apparatus disclosed in the patent literature 1 has a structure to perform negative feedback such that the pixel current corresponds to the image signal. Thus, even if a current control circuit has variations in an input voltage vs. output current characteristic, such variations are absorbed, and the pixels are provided with the same current value with respect to a prescribed image signal. The display apparatus of the patent literature 2 is disclosed having a structure that the light emitted from the light emitting section is detected by a photodiode and fed back to the image signal. Thus, it is conceivable that the substantially the same effects can be obtained.                [Patent Document 1] Japanese Patent Laid-Open Application No. 2002-91377        [Patent Document 2] Japanese Patent Laid-Open Application No. 2003-271098        
But, the structure disclosed in the patent literature 1 might have a disadvantage in view of an aperture ratio (a ratio of the net area of the light emitting section to the display area) of the display because it is essentially necessary to form an error amplifying circuit, which is required for negative feedback, on the individual pixels. And, it is conceivable that the structure disclosed in the patent literature 2 is inevitably complex because a reset circuit and a reset signal path are required to obtain the above-described feedback signal.